Dirichlet 1837: primes in (a, a+d, a+2d, ...) coprime to a appear infinitely-often. Proof via L(s, χ) for non-trivial Dirichlet-character χ. Modern: Linnik 1944 + Heath-Brown.
Dirichlet 1837: primes in (a, a+d, a+2d, ...) coprime to a appear infinitely-often. Proof via L(s, χ) for non-trivial Dirichlet-character χ. Modern: Linnik 1944 + Heath-Brown.